It is described in Patent Literatures 1 to 3 as a prior art that right and left travel crawlers are installed in a rear portion of a machine body in a travel vehicle such as a tractor, that is, right and left front wheels are installed in a front portion of the machine body, and the right and left travel crawlers are installed in the rear portion of the machine body.
The prior art is a structure in which a rear axle is pivoted to a rear axle case of a travel machine body, a drive wheel body is attached to the rear axle, a track frame extending in a back and forth direction is arranged at a position which is below the rear axle case, and a travel crawler is installed to the track frame, wherein an approximately midstream portion in the back and forth direction of the track frame is rotatably pivoted to the travel machine body side such as the rear axle case by one oscillation supporting point shaft which is arranged at a position which is at an appropriate distance below the rear axle, and the track frame is structured such that a front portion and a rear portion thereof move up and down in a reverse direction to each other. The travel machine body is structured such as to be moved forward or moved backward by winding a travel crawler in an approximately triangular shape around a front driven wheel body which is provided in a front end side of the track frame, a rear driven wheel body which is provided in a rear end side, and the drive wheel body, and rotating the travel crawler by the drive wheel body.